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Alarms should be provided on a gas turbine. The standards call for alarmsto be provided to indicate malfunction of oil and fuel pressure， high exhausttemperature， high differential pressure across the air filter， excessive vibra-tionlevels， low oil reservoir levels， high differential pressure across oil filters， and high oil drain temperatures from the gearings. Shutdown occurs withlow oil pressure， high exhaust temperature， and combustor flameout. It is recommended that shutdown also occur with high thrust bearing tempera-tures and with a temperature differential in the exhaust temperature. Vibra-tion detectors suggested in the standards are noncontacting probes.Presently， most manufacturers provide velocity transducers mounted on thecasing， but these are inadequate. A combination of noncontacting probes and accelerometers are needed to ensure the smooth operation and diagnostic capabilities of the unit.
Fuel systems can cause many problems， and fuel nozzles are especiallysusceptible to trouble. A gaseous fuel system consists of fuel filters， regula-tors， and gauges. Fuel is injected at a pressure of about 60 psi (4 Bar) above the compressor discharge pressure for which a gas compression system isneeded. .nockout drums or centrifuges are recommended， and should be implemented to ensure no liquid carry-overs in the gaseous system.
Liquid fuels require atomization and treatment to inhibit sodium and vanadium content. Liquid fuels can drastically reduce the life of a unit if not properly treated. A typical fuel system is shown in Figure 4-7. The effect of fuels on gas turbines and the details of types of fuel handling systems is given in chapter 12.
Recommended materials are outlined in the standards. Some of the recommendations in the standard are carbon steel for baseplates， heat-treated forged steel for compressorwheels， heat-treated forged alloy steelfor turbinewheels， and forged steel for couplings. The growth of materials technology has been so rapid especially in the area of high temperature materials the standard does not deal with it. Details of some of the materials technology of the high temperature alloys and single crystal blades are dealtwith in chapters 9 and 11. However， the standards call for blading， whichmust have at least8，000 trouble-free operating hours in similar operating conditions.
The vendor is required to present campbell and Goodman diagrams for the blading backed by demonstrated experience in the application of iden-tical blades operating with the same source or frequency of excitation that is present in the unit. The vendor shall indicate on the Goodman diagrams the standard acceptance margins. chapter 11 deals with the Goodman diagram for materials. All campbell diagrams shall show the blade frequencies thathave been corrected to reflect actual operating conditions.认here applicable， the diagrams for shrouded blades shall show frequencies above and below the blade lock-up speed and shall specify the speed at which blade lock-upoccurs. chapter 5 goes into details of the campbell diagram， and chapter 16 deals with the types of signals emitted by the resonance of blades.
The tips of rotating blades and the labyrinths of shrouded rotating blades shall be designed to allow the unit to start up at any time in accordance withthe vendor.s requirements.认hen the design permits rubbing during normalstartup， the component shall be designed to be rub tolerant and the vendor shall state in his proposal if rubbing is expected.
The blade natural frequencies shall not coincide with any source of excitation from 10% below minimum governed speed to 10% above maximum continuous speed. If this is notfeasible， blade stress levels developed at any specified driven equipment operation shall be low enough to allow unrestricted operation for the minimum service life. Blades shall be designed to withstand operation at resonant frequencies during normal warm-up. Speeds below the operation range corresponding to such blade resonance should be clearly specified.
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本文链接地址：燃气涡轮工程手册 Gas Turbine Engineering Handbook 1(62)
